Singer-songwriter Joni Mitchell is in intensive care after being found unconscious at her Los Angeles home.
The 71-year-old was rushed to hospital on Tuesday afternoon. It is not immediately clear what illness she has.
A statement released on her website said she "regained consciousness on the ambulance ride to an LA area hospital".
The Canadian-born artist is "currently in intensive care undergoing tests and is awake and in good spirits," it added.
Los Angeles fire officials said paramedics had answered a 911 call in Bel Air, where Mitchell lives, and had taken a patient whom they did not identify to hospital.
In December she told Billboard magazine that she had a rare skin condition, Morgellons disease, which prevented her from performing.
"I can't sing any more - don't miss it. I can't play any more - don't miss it. I've got all these instruments laying around and hopefully one day I'll pick them up," she was quoted as saying.
Morgellons is a controversial condition and is not recognised by mainstream medical authorities. Sufferers say it is characterised by crawling and stinging sensations under the skin but many in the medical community believe it is a psychiatric disorder.
"No. Not Joni"
Musicians took to social media to send messages of support. Boy George tweeted: "A prayer for Joni Mitchell."
Billy Idol also sent best wishes: "Sorry to hear today's news about Joni Mitchell. I sang on her 'Dancing Clown' single many moons ago, all the best 4 her recovery."
Mitchell has released 19 original albums, with her last in 2007.
Best known for her 1970 hit Big Yellow Taxi, Mitchell was inducted into the Rock and Roll Hall of Fame in 1997.
Her 1971 album, Blue, is ranked 30th on Rolling Stone magazine's list of the 500 Greatest Albums of All Time.